The overall objective of our research is to understand the course of differentiation of human erythroid cells in terms of membrane glycoproteins and to evaluate cell membrane glycoproteins as onco-differentiation cell surface markers shared by tumor cells and normal cells at an early stage of differentiation. Two major aspects deal with: (1) Testing whether certain membrane glycoproteins can function as tumor-specific markers as well as normal immature cells. We have found that tumor promoters diminish the expression of glycophorin on K562 cells and HEL cells. The results indicate that the expression of glycophorin is closely related to the status (immature or macrophage-like cells) of cells treated by tumor promoters. Further studies indicate that these decreases are due to the decrease of de novo synthesis. Experiments are in progress to assess whether the decrease is caused by transcriptional or translational regulation. (2) Clarifying structural change of lactosaminoglycan throughout the various ontogenic and oncogenic stages. We have found that lactosaminoglycan displays a drastic structural change during ontogenesis and differentiation. We have recently elucidated the structure of lactosaminoglycans present in human neonatal and adult erythrocytes with the help of a newly developed technology, fast atom bombardment mass spectrometry. The results revealed distinct changes in lactosaminoglycans during development from fetal to adult erythrocytes. Further studies will elucidate the structures of lactosaminoglycans isolated from human erythroleukemic cells. (M)